Description of the Related Art
Conventional nonvolatile memory devices using resistance materials may include PRAM (Phase change Random Access Memory), RRAM (Resistive RAM), and MRAM (Magnetic RAM). Nonvolatile memory devices using resistance materials may store data using phase-change materials such as chalcogenide alloy (PRAM), variable resistive elements (RRAM), and MTJ (Magnetic Tunnel Junction) thin films according to the magnetization state of a ferromagnetic substance.
A phase change memory cell including the phase change material may change into a crystal state or amorphous state by cooling after heating. Since the phase change material in the crystal state has a low resistance and the phase-change material in the amorphous status has a high resistance, the crystal state may be defined as set data 0, and the amorphous state may be defined as reset data 1.
The conventional phase change memory cell may include a variable resistive element containing a phase change material and an access element that controls current that flows through the variable resistive element. A transistor or diode can be used as an access element. The phase change memory cell that uses the transistor as an access element is called a transistor-controlled PRAM cell, and the phase change memory cell that uses diode as an access element is called a diode-controlled PRAM cell.